Degradation in Field-aged Crystalline Silicon Photovoltaic Modules and Diagnosis using Electroluminescence Imaging

Degradation phenomena observed in field-aged crystalline silicon photovoltaic modules include EVA browning, delamination between the glass-encapsulant and the cell-encapsulant interfaces, degradation of the anti-reflective coating, corrosion of busbars and contacts, cracks, humidity ingress, etc. The type and severity of the defects observed vary significantly between cells, modules and installations as affected by a number of both internal and external parameters. This study presents mild to severe degradation effects observed in crystalline silicon PV modules operating outdoors for different periods of time and investigated through non-destructive testing techniques including I-V characterisation, UV fluorescence, IR thermography and Electroluminescence (EL) Imaging. The identification and diagnosis of defects and further correlation to the electrical degradation of the module is achieved through the complementary contribution of these techniques. Severe electrical degradation and mismatch between the cells are identified through IR thermography and EL imaging. Diagnosis of rather uniformly degraded modules is enhanced through EL Imaging by which shunts, higher resistance regions, cracks, broken metallization are identified, while the module may appear to operate reliably. Signs of early degradation are further diagnosed through UV fluorescence and EL Imaging, allowing to monitor the evolution of defects and evaluate module reliability

Intelligent energy buildings based on RES and Nanotechnology

The paper presents the design features, the energy modelling and optical performance details of two pilot Intelligent Energy Buildings, (IEB). Both are evolution of the Zero Energy Building (ZEB) concept. RES innovations backed up by signal processing, simulation models and ICT tools were embedded into the building structures in order to implement a new predictive energy management concept. In addition, nano-coatings, produced by TiO2 and ITO nano-particles, were deposited on the IEB structural elements and especially on the window panes and the PV glass covers. They exhibited promising SSP values which lowered the cooling loads and increased the PV modules yield. Both pilot IEB units were equipped with an on-line dynamic hourly solar radiation prediction model, implemented by sensors and the related software to manage effectively the energy source, the loads and the storage or the backup system. The IEB energy sources covered the thermal loads via a south façade embedded in the wall and a solar roof which consists of a specially designed solar collector type, while a PV generator is part of the solar roof, like a compact BIPV in hybrid configuration to a small wind turbine

PV cell and module degradation, detection and diagnostics

With crystalline silicon photovoltaic (PV) modules being on the market for over 3 decades, investigation into usual causes and extent of module degradation after prolonged exposure in field conditions is nowadays possible. Degradation phenomena vary significantly between cells, modules and installations, giving rise to different power degradation rates reported. The main defects that have been observed in field aged PV modules, include EVA browning, degradation of the anti-reflective coating, delamination between the glass-encapsulant and the cell-encapsulant interfaces, humidity ingress, corrosion of busbars and contacts, shunt paths, cracks/ micro-cracks in the cell, damage of the glass and the back sealing, and bypass diode failure. This study presents severe degradation effects observed in PV modules operating outdoors for over 20 years. In many of the cases investigated different defects were seen to coexist within the same cell or module, leading to more severe effects of optical/physical, thermal, and electrical degradation phenomena significantly reducing the PV power output. Other modules which exhibited extensive optical/physical degradation showed milder degradation in performance. Detection of module degradation was carried out in this study first through visual inspection and I-V curve analysis. Further non-destructive diagnostic techniques were used such as infrared thermography for the identification of hot spots, that were seen to be mainly linked to resistive busbars and contacts, and electroluminescence imaging for the identification of shunts and other defects. The detection, diagnosis and monitoring of such defects is of great importance for a deeper understanding of the complex ageing mechanisms that take place after prolonged PV exposure in field conditions, and the identification of underlying causes, assisting the early identification of defects and the extension of the energy life of PV systems

TiO2-based nanocoating with self-cleaning and anti-reflective properties: effects on PV performance

Photovoltaic modules operating in field conditions exhibit a significant reduction in their power output due to dust accumulated on their surface. Depending on the amount of dust accumulated the reduction in peak power has been reported in the range of 5-15%. The accumulated dust is linked to meteorological and environmental parameters such as humidity, precipitation, solar radiation, ambient temperature, dusty winds, air pollution, etc., but also to the location and surroundings of the installation and the period for which the PV modules have been left without cleaning. To reduce the effect of dust, research has been recently focused on coatings with self-cleaning properties that may be applied on PV glass surface. Also, coatings with spectral selective properties have been investigated to enhance PV performance. The purpose of this study is to examine the effect of a nanocoating with self-cleaning and anti-reflective properties on the performance of a PV module when applied on its glass surface. Particular interest is given to its anti-reflective properties which are assessed for angles-of-incidence of solar radiation greater than 40o, where reflectance is generally higher. The performance of two same PV modules one with and one without the coating is compared

Self-cleaning properties of TiO2/palygorskite and TiO2/halloysite nanocomposite coatings

Tubular halloysite and microfibrous palygorskite clay mineral combined with nanocrystalline TiO 2 are involved in the preparation of nanocomposite films on glass substrates via sol-gel route at 450°C. The synthesis employing nonionic surfactant molecule as pore directing agent along with the acetic acid-based sol-gel route without addition of water molecules. Drying and thermal treatment of composite films ensure elimination of organic material lead to the formation of TiO 2 nanoparticles homogeneously distributed on the palygorskite and halloysite surfaces. Nanocomposite films without cracks of active anatase crystal phase on palygorskite and halloysite surfaces are characterized by microscopy techniques, UV-Vis spectroscopy, and porosimetry methods in order to examine their structural properties. The composite palygorskite- TiO 2 and halloysite/ TiO 2 films with variable quantities of palygorskite and halloysite were tested as photocatalysts in the photo-oxidation of Basic Blue 41 azo dye in water. These nanocomposite films proved to be most promising photocatalysts and highly effective to dye’s decoloration in spite of small amount of palygorskite/ TiO 2 or halloysite/ TiO 2 catalyst immobilized onto glass substrates

A PV temperature prediction model for BIPV configurations, comparison with other models and experimental results

The temperatures of c-Si and pc-Si BIPV configurations of different manufacturers were studied when operating under various environmental conditions. The BIPV configurations formed part of the roof in a Zero Energy Building, (ZEB), hanged over windows with varying inclination on a seasonal basis and finally two identical 0.5kWp PV generators were mounted on a terrace in two modes: fixed inclination and sun-tracking. The PV and ambient temperatures, Tpv and Ta, respectively, the intensity of the global solar radiation on the modules, IT, and the wind velocity on their surface, vw, were monitored for 2 years. The effect of the intensity, IT, the PV module inclination and vw, on Tpv was investigated. The values of the coefficient f relating Tpv and IT, were determined and argued for the configurations studied. A theoretical model was elaborated to predict Tpv and f for the cases of PV modules embedded on a roof, hanging over the windows and in free standing configurations. The effect of vw on f dominated for PV modules mounted on the terrace compared to the BIPV configurations in wind protected areas

An embedded microcontroller unit for PV module monitoring and fault detection

This paper presents the architectural lay-out and functional design details of a microcontroller embedded electronic monitoring system (e-EMS). According to the design, this unit is integrated into the PV module junction box. It can be scaled up to form part of a complex PV power plant control system. The communication topology follows a 3-tier structure. It uses two processors, one dedicated for data acquisition and the other for communication purposes. The e-EMS provides a complete set of data associated to PV module performance characteristic parameters, including current and voltage of the PV module and each sub-string of cells, operation of the bypass diodes along with the corresponding current and voltage measurements, PV temperature and environmental parameters. The sampling rate can be programmed in a large range from 1 to 65s along with the number of samples used for averaging signal values. The power output is determined every hour, as a basic output of the system. Comparison of the determined values with the expected ones when normalized to the PV operating conditions provides reliable information on deviation trends, the degree of degradation that the PV module experiences, while the analysis of the sampled data may identify the cells or modules which experience degradation and disclose types of factors which affect their operation

A New Dynamic Model to Predict Transient and Steady State PV Temperatures Taking into Account the Environmental Conditions

Photovoltaic (PV) cell and module temperature profiles, Tc and Tpv, respectively, developed under solar irradiance were predicted and measured both at transient and steady state conditions. The predicted and measured Tc or Tpv covered both a bare c-Si PV cell, by SOLARTEC, at laboratory conditions using a solar light simulator, as well as various c-Si and pc-Si modules (SM55, Bioenergy 195W, Energy Solutions125W) operating in field conditions. The time constants, τ, of the Tc and Tpv profiles were determined by the proposed model and calculated using the experimentally obtained profiles for both the bare PV cell and PV modules. For model validation, the predicted steady state and transient temperature profiles were compared with experimental ones and also with those generated from other models. The effect of the ambient temperature, Ta, wind speed, vw, and the solar irradiance, IT, on the model performance, as well as of the mounting geometries, was investigated and incorporated in the prediction model. The predicted temperatures had the best matching to the measured ones in comparison to those from six other models. The model developed is applicable to any geographical site and environmental conditions

Dynamic load management and optimum sizing of stand-alone hybrid PV/Wind system.

Simulation algorithms for the sizing of stand-alone hybrid PV/Wind systems are a powerful tool in evaluating the optimum configuration that would cover the energy demand with a predefined reliability level at the lowest cost. Several parameters such as the interval of the simulation (day, day-night, hourly) and the consumption profile may significantly affect the optimum configuration. This paper examines the effect of these parameters within an optimum sizing simulation algorithm developed. The effect of these parameters was particularly evident at low battery capacities, which involve optimum configurations resulting in minimum cost. Furthermore, shift-able loads in the hourly-based weekly profile assumed in this study were identified, and a dynamic load management functionality was developed. In this approach, loads that could be shifted through time were dynamically allocated during periods of excess energy production by the hybrid PV/Wind system. The results showed an increase in system reliability from 95% to 97% when load shifting was introduced. Finally, sizing the system for only the static (non-shift-able loads) proved to withstand the addition of the extra shift-able loads while retaining the 95% reliability level when the load management functionality was introduced. Thus, a smaller installation with lower cost is achieved